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Abstract

Background

Understanding how the determinants of behaviour vary by context may support the design
of interventions aiming to increase physical activity. Such factors include independent
mobility, time outdoors and the availability of other children. At present little
is known about who children spend their time with after school, how this relates to
time spent indoors or outdoors and activity in these locations. This study aimed to
quantify who children spend their time with when indoors or outdoors and associations
with moderate to vigorous physical activity (MVPA).

Methods

Participants were 427 children aged 10–11 from Bristol, UK. Physical activity was
recorded using an accelerometer (Actigraph GT1M) and matched to Global Positioning
System receiver (Garmin Foretrex 201) data to differentiate indoor and outdoor location.
Children self-reported who they spent time with after school until bed-time using
a diary. Each 10 second epoch was coded as indoors or outdoors and for ‘who with’
(alone, friend, brother/sister, mum/dad, other grown-up) creating 10 possible physical
activity contexts. Time spent and MVPA were summarised for each context. Associations
between time spent in the different contexts and MVPA were examined using multiple
linear regression adjusting for daylight, age, deprivation and standardised body mass
index.

Results

During the after school period, children were most often with their mum/dad or alone,
especially when indoors. When outdoors more time was spent with friends (girls: 32.1%;
boys: 28.6%) than other people or alone. Regression analyses suggested hours outdoors
with friends were positively associated with minutes of MVPA for girls (beta-coefficient
[95% CI]: 17.4 [4.47, 30.24]) and boys (17.53 [2.76, 32.31]). Being outdoors with
brother/sister was associated with MVPA for girls (21.2 [14.17, 28.25]) but not boys.
Weaker associations were observed for time indoors with friends (girls: 4.61 [1.37,
7.85]; boys: (7.42 [2.99, 11.85]) and other adults (girls: 5.33 [2.95, 7.71]; boys:
(4.44 [1.98, 6.90]). Time spent alone was not associated with MVPA regardless of gender
or indoor/outdoor location.

Conclusions

Time spent outdoors with other children is an important source of MVPA after school.
Interventions to increase physical activity may benefit from fostering friendship
groups and limiting the time children spend alone.

Keywords:

Background

Physical activity during childhood confers health benefits throughout the lifespan
[1,2]. Children aged 5–18 are recommended to engage in at least one hour of moderate-to-vigorous
physical activity (MVPA) per day [3], but the majority of children in the UK do not meet this target [4,5]. Consequently the development and implementation of policies and programmes to change
this behaviour is a major public health priority. The development of such strategies
relies upon an understanding of the factors influencing physical activity [6]. Research investigating the correlates and determinants of physical activity can
help identify target groups in need of intervention, and highlight mediating variables
which could be manipulated to change behaviour [7]. However, this process is complex because physical activity is not a single action
but a class of varied behaviours [8], and different types of physical activity have been demonstrated to have different
determinants [9-11]. Consistent with an ecological approach to understanding health behaviours [12], it is also important to consider the environmental context (i.e. location, time
period, other participants) in which physical activity occurs [9]. Describing the value of different environmental and social settings for physical
activity could inform context-specific interventions [13]. One contextual characteristic which could influence children’s physical activity
is who children spend their leisure time with. Leisure time is a key source of children’s
physical activity, especially during the ‘critical hours’ immediately after school
[14]. After school leisure time may be spent alone, with brother/sister, with friends,
with mum/dad or other grown-ups. It is plausible that who children spend their time
with influences the duration, intensity and types of physical activity they engage
in [15]. However, little is known about who children spend their time with after school,
or how this is associated with their level of MVPA.

It is well established that the time children spend outdoors is more actively spent
than time spent indoors [16,17]. At present it is unclear whether this time is spent alone, supervised by adults,
or with other children. Time spent unsupervised by adults is thought to contribute
significantly to children’s daily physical activity [18], while freedom from adult rules and structure is an important feature of active free
play [19]. In addition, child directed play has the potential to provide unique emotional,
social and cognitive benefits [20]. However, it is suggested that children’s, and in particular girls’ independent physical
activity is increasingly limited due to parental concerns about safety [21-24]. Since independent mobility is consistently associated with children’s physical activity
[25-27], it is important to quantify how much unsupervised outdoor time children are afforded.
Time spent with friends and siblings and the availability of other children to play
with have been reported to be key influences on children’s participation in unstructured
outdoor physical activity [18,28-30]. These relationships may be of particular importance for children at the transition
from primary to secondary school, as it is at approximately this age that independence
from adults starts to develop [28,31].

To date, mostly qualitative and self or proxy report data have been used to characterise
children’s indoor and outdoor after school leisure time physical activity. Objective
information from Global Positioning System (GPS) receivers and accelerometers can
more accurately quantify time spent indoors and outdoors in relation to physical activity
[17]. Combining this with diary data reporting who children spend their time with provides
a unique data set to describe a potentially important context for how physical activity
may be modified. Consequently, the aim of this study is to use combined diary, GPS
and accelerometer data to investigate who children spend their indoor and outdoor
time with, and how this relates to MVPA after school. It is hypothesised that children’s
MVPA accrual will vary by context, and that time spent outdoors with friends or siblings
will exhibit stronger positive associations with MVPA than time spent in other contexts.

Methods

This study used baseline data from the PEACH (Personal and Environmental Associations
with Children's Health) project. Between September 2006 and July 2008 the project
recruited 1,307 year six (age 10-11 yrs) children from 23 state primary schools in
Bristol, UK. The methods of the PEACH project have been described fully elsewhere
[25]. Written informed consent was obtained from a parent/guardian of all children who
took part in the study. The study was carried out in accordance with the Declaration
of Helsinki and ethical approval was provided by University of Bristol Ethics Committee.

Physical activity

Physical activity intensity was summarised at ten second epochs using an accelerometer
(GT1M; ActiGraph LLC, FL, USA). Participants were asked to wear the accelerometer
on a waist belt for seven continuous days. The method of Troiano, Berrigan, Dodd et
al. was used to identify accelerometer non-wear time: periods of 60 minutes (or more)
of zero values were discarded allowing for up to two minutes of non-zeros per hour
[32]. This criterion was used in preference to shorter non-wear definitions (e.g. 10 or
20 minutes) which can result in unnecessary removal of data and underestimation of
sedentary time in some subgroups, for example those who are overweight [33]. For inclusion in analyses participants were required to have recorded at least three
hours of after school accelerometer data on at least one weekday.

Indoor/outdoor location

Positional data were recorded every ten seconds using a GPS receiver (GPS; Garmin
Foretrex 201) [34]. Participants wore the GPS receiver between the end of school and bedtime on four
consecutive school days. Participants were trained to turn the GPS receiver on at
the end of school and off at bedtime. Research staff charged the units on day three
of use due to limited battery life. Days with no GPS data were removed from the dataset.

Diary data

Participants were asked to complete a one day recall diary for three school days.
This diary was based on previous work [35,36]. The children were asked to record the start and end time of after school activities
starting with the first thing they did after leaving school. In addition to the start
and end time, participants were asked to select who they were with for each activity
from five options: on my own, with friend, with brother/sister, with mum or dad, with
another grown up. To maximise the quality of the diary provided by the children, an
annotated example was provided and explained verbally by the researcher to small groups
of participants (<10). Participants were incentivised to complete diaries via vouchers
provided for completion of all measures and personal prompts were provided by researchers
and teachers to remember to complete diaries. Periods with no diary record were quantified
and children who did not provide diary data on at least one day were excluded from
analyses.

Confounding variables

Height (m) and weight (kg) were measured using a stadiometer (SECA) and digital scales
(indoor clothing, shoes removed). Body mass index (BMI) was calculated (body mass
in kg divided by height in metres squared), and BMI standard deviation score (BMISDS)
was derived from standard tables [37]. Age, sex and post-code were confirmed by the Local Education Authority. Minutes
of daylight from 15:00 until sunset for the day of measurement were determined using
standard tables [38]. The UK Index of Multiple Deprivation (IMD) 2007 score was defined using full home
postcode.

Data processing

Ten second epoch accelerometer and GPS data were matched using date and time stamps
for the period between 15:00 and 22:00 on weekdays using STATA (version 12.0, College
Station, TX) as previously described [17]. Ten second epochs with accelerometer activity counts exceeding 383 (2296 counts
per minute/6) were coded as MVPA [39,40]. The GPS receiver used in this study does not record positional data when inside
a building. Consequently each epoch of accelerometer data with no corresponding GPS
record was defined as indoors, while GPS matched accelerometer data were defined as
outdoors. The delay between exiting a building and GPS signal acquisition can be as
much as 45 seconds likely resulting in underestimation of time outdoors [17,41]. Any GPS point with a speed of greater than 15 kph was excluded as this was likely
to represent an aberrant signal (e.g. reflection from a building) or motorised transportation
[42].

Epochs with GPS and accelerometry data but no matching diary data entries were removed
from the analyses. Participants who did not provide combined accelerometer, GPS and
diary data on at least one day were excluded from analyses. In addition, some children
provided diary entries with overlapping times and these were also excluded (<1% of
total). Total minutes spent and minutes of MVPA were summed according to who children
were with and whether they were indoors/outdoors. For example all epochs classified
as ‘indoors’ and ‘with mum or dad’ were summed to give the time spent indoors with
mum/dad, and the MVPA recorded during that time. This resulted in ten (indoors/outdoors:
on own, with friend, with brother/sister, with mum/dad, with other grown-up) distinct
contexts of after school physical activity.

Data analyses

Descriptive statistics (mean, standard deviation and percentage) of total time and
time in MVPA were calculated by sex, social company and location (indoors/outdoors).
Multiple linear regression models were used to assess the contribution of time in
each context to the total minutes of after school MVPA. This was expressed as the
mean increase in minutes of MVPA for each hour spent in that context after adjusting
for time spent in all the other contexts. In addition models were adjusted for potential
a priori confounders (age, BMISDS, IMD, daylight hours). Due to well-established gender differences
in daily physical activity, data for girls and boys were analysed separately [43]. Visual inspection of standardised residuals against predicted scores indicated some
heteroskedacity and so robust (Huber-White) standard errors are reported. All analyses
were conducted using Stata/SE (version 12.0, College Station, TX).

Results

The sample consisted of 230 girls and 197 boys with mean age 10.7 (SD = 0.5) years
and BMI 18.3 (SD = 3.2) kg/m2 who provided combined GPS, accelerometer and diary data on at least one measurement
day. Overall, girls recorded 21.7 (SD = 12.3) minutes of MVPA (including data recorded
both indoors and outdoors) during the after school period while boys recorded 25.0
(SD = 13.4) minutes. The GPS data estimated that girls spent 21.0 (SD = 27.7) minutes
outdoors after school while boys were outdoors for 20.3 (SD = 27.4) minutes during
the same period. Matched accelerometer and GPS data suggested that girls recorded
4.3 (SD = 6.4) minutes or 19.8% of total after school MVPA outdoors, while for boys
this value was 4.6 (SD = 7.1) minutes or 18.4%. Girls provided a mean of 155.6 (SD = 71.9)
minutes of after school diary information, and this was time-matched to accelerometer
data which included on average 13.4 (SD = 9.3) minutes of MVPA. Boys provided a mean
of 160.1 (SD = 74.5) minutes of after school diary information, and this was time
matched to accelerometer data which included on average 15.6 (SD = 11.1) minutes of
MPVA. Of all the valid after school accelerometer data, 40.5% of girls’ and 38.3%
of boys’ accelerometer epochs could not be time matched to diary records because no
diary entries had been recorded by the children during these periods. Consequently,
37.0% of girls’ and 36.0% of boys’ accelerometer recorded MVPA was not described by
the participants in their diary. Table 1 reports the proportion of accelerometer epochs that were matched to GPS data (subsequently
labelled outdoors), and the proportion of accelerometer epochs matched to a diary
record, by hour.

Table 1.Proportion of accelerometer epochs matched to GPS and diary records by hour

Total time spent and MVPA

Using the available combined accelerometer, diary and GPS data, Table 2 (girls) and Table 3 (boys) summarise the time spent and MVPA recorded according to who children were
with (from diary data) and whether they were indoors or outdoors after school (from
GPS data). Both girls (28.9%) and boys (28.3%) recorded more time with their mum/dad
than other categories, followed by time spent alone (girls: 21.9%; boys: 24.6%). Girls
spent least time with brother/sister (13.9%), while boys spent least time with other
grown-ups (14.1%). Boys recorded the most MVPA when with their friends or mum/dad
(both 25.0%), while girls recorded the most MVPA when with their mum/dad (23.9%).

Table 2.Girls' after school time and MVPA by who they were with and indoor or outdoor location

Table 3.Boys’ after school time and MVPA by who they were with and indoor or outdoor location

Time spent in different contexts

The greatest share of time outdoors was spent with friends (girls: 32.1%; boys: 28.6%),
followed by mum/dad (girls: 20.7%; boys: 27.1%). Both girls (2.9%) and boys (2.6%)
spent a small percentage of the total after school period outdoors with friends. Amongst
girls, the smallest proportion of time outdoors was spent with brother/sister (12.1%);
while for boys least time outdoors was spent with other grown-ups (10.7%). Children’s
time indoors was mostly spent with mum/dad (girls: 29.8%; boys: 29.5%) or by themselves
(girls: 22.1%; boys: 26.3%). Only 14.4% of girls’ and 15.0% of boys’ indoor time was
spent with friends.

MVPA recorded in different contexts

Both girls (32.2%) and boys (38.7%) most commonly recorded outdoor MVPA in the presence
of friends. Least outdoor MVPA was recorded with brother/sister (girls: 12.9%; boys
9.7%) or other grown-ups for boys (9.7%). Indoor MVPA was more evenly distributed,
although for both girls (25.2%) and boys (30.1%) this was most commonly recorded with
mum/dad.

Associations between time in specific contexts and after school MVPA

Table 4 (girls) and Table 5 (boys) contain data from multiple linear regression models examining relationships
between hours spent in specific contexts and minutes of after school MVPA. The models
explained 34.4% of girls’ and 30.1% of boys’ variance in after school MVPA. For both
girls and boys, outdoor contexts exhibited stronger associations with MPVA than indoor
contexts. Time spent outdoors in the company of friends was particularly important
for both boys and girls, with an increase of approximately 17 minutes of MVPA recorded
for every additional hour spent in this context. Similarly, when girls spent time
outdoors with siblings, they recorded on average 21.21 minutes of MVPA each hour.
This relationship was similar for boys but non-significant. When indoors, time with
friends was positively associated with MVPA, however relationships were weaker than
when outdoors (4.61 and 7.42 minute increase in MVPA accrued per hour for girls and
boys respectively). Relationships of similar direction and magnitude to these were
also observed between time indoors with other grown-ups and MVPA for both girls and
boys. Time spent alone either indoors or outdoors was not associated with MVPA regardless
of gender.

Table 4.Multiple linear regression of time in specific contexts and total after school MVPA
amongst girls (n = 230)

Table 5.Multiple linear regression of time in specific contexts and total after school MVPA
amongst boys (n = 197)

Discussion

The main findings of this study are that who children spend time with after school
is an important influence on physical activity, and that in particular, time spent
outdoors with other children is a key context for participation in MVPA. Previous
studies have investigated children’s independent mobility and independent physical
activity, demonstrating that greater license to leave the home unaccompanied is positively
associated with time outdoors [27] and physical activity [25]. This work builds upon those findings by quantifying the time children spend alone,
with adults, or with other children, and matching this with objective measures of
physical activity and indoor/outdoor location. Participants reported spending most
time alone or with their parents, especially during indoor time which was very rarely
spent with other children. Although children spent few minutes outdoors after school,
when they were outdoors they were most likely to be with friends. The accumulation
of long periods spent indoors alone or supervised by adults and comparatively little
time spent outdoors with other children supports the view that there are limited opportunities
for primary school children to go outdoors without an adult [24,44]. This is concerning given that independent mobility has an established association
with children’s physical activity [25-27], and that time outdoors is approximately three times more likely to spent engaging
in MVPA [17].

It has been reported in other UK-based studies that approximately one third of children
are only allowed outdoors without an adult when in the company of other children [15]. Previous work also suggests that neighbourhood relations and friends are linked
to perceptions of safety for both parents and children [45,46]. Neighbourhood relations and having someone to play with may also positively influence
parental decisions about independent mobility [26]. However, from the present cross sectional data it is not possible to distinguish
whether time outdoors facilitates being with friends, or whether the companionship
of other children is a pre-requisite of parents’ willingness to grant independent
mobility. Parents may be vulnerable to a cycle of increased safety concerns linked
to limited independent mobility and the subsequent social norm of children not being
allowed out to play in the local environment [47,48]. Valentine & McKendrick [24] suggest that a move from public play to organised forms of physical activity has
prompted suspicion of those children in public space without adults. Similarly, Ergler,
Kearns & Witten [48] report that the normalisation of indoor play is especially pronounced in urban areas
because children are unable to use informal areas such as sidewalks. The regression
analyses report that alongside outdoor time with friends, indoor time with friends
was also positively associated with MVPA. Time spent with other children therefore
appears crucial for physical activity, and this is augmented by being outdoors. Recently
published longitudinal data report that an increase in the number of friends between
primary and secondary school is associated with an increase in girls MVPA [49]. Further longitudinal work is necessary to understand whether the formation of friendship
groups is a product of, or fundamental determinant for independent mobility and outdoor
physical activity. Based on such work it may be possible to promote physical activity
by developing neighbourhood community links amongst children and parents, and seeking
to restore the social norm of children using the outdoors as a setting for physical
activity.

Parents are reported to be more protective of girls due to greater perceived risk
and to subsequently limit their independence [21,22,50]. This paper supports this position indicating that indoor contexts are more important
for girls’ physical activity than for boys’. Time spent indoors with friends was important
for both genders, however periods indoors with siblings or parents were only associated
with MVPA amongst girls. These findings echo qualitative work by Brockman, Fox & Jago
[51] which reported that girls were more likely to report active play centred on the home
and with family members. Previous research has reported that similar numbers of boys
and girls are allowed outdoors without an adult, but that for girls this was more
likely to be conditional on other children being present [15]. The strength of association between time spent outdoors with friends or siblings
and MVPA in this study supports the hypothesis that girls who do have other children
to accompany them outdoors are likely to be more active. Thus while safety in numbers
and fostering friendship groups may be important to facilitate after school MVPA [49], it is encouraging that despite their limited independence girls appear to find ways
to be active indoors. These findings tie with those of Atkin, Gorely, Biddle et al.
[14] who found that technology based sedentary behaviour during the ‘critical hours’ was
higher amongst boys than girls. Future research and interventions may benefit from
not only increasing the time children spend outdoors with others, but also seeking
to maximise the potential of indoor environments for physical activity and limiting
the time children spend alone.

It is not clear why time outdoors with friends is a particularly valuable source of
MVPA. It may be due to the freedom from adult rules and structure [19,52]. Alternatively, it is possible that children’s movement patterns and behaviours vary
depending on whether they are with adults or other children. It has been reported
that children’s movement is more meandering when away from adults [15], and some children like to do activities (such as non-permitted behaviours) outside
the view of adults [53]. This paper emphasises the importance of time spent with other children, however
it should also be highlighted that many children rely on adults to supervise their
activity. Strategies and policy that enable adults to supervise physical activity
and encourage families to be active together may be beneficial for individuals across
the lifespan. This study also suggests that time spent indoors with adults other than
mum/dad is positively associated with MVPA for both boys and girls, and this may be
indicative of after school supervision. It is necessary to understand more about what
behaviours indoors contribute to MVPA and how these may be manipulated to increase
opportunities for physical activity. For example, after school clubs offer a safe
indoor environment for physical activity but opportunity for this may be limited due
to the inclusion of academic and snack times [54].

Strengths and limitations

A key strength of this study is the combination of accelerometer, GPS and diary data
to describe the context of children’s physical activity. This allowed exploration
of not only who children spend their time with, but whether this related to objectively
measured location (indoors vs. outdoors) and physical activity. Whilst the sample
size was large and was drawn from a number of different primary schools representing
a large English city, the results may not be generalisable to other locations or age
groups. Furthermore, given that only children who provided matched accelerometer,
GPS and diary data were included, the sample may not be wholly representative of the
wider population. Some included participants only provided one day of combined data
which may limit the reliability of the findings, however the methodology developed
and the rich context-specific nature of the physical activity data provide valuable
insight into children’s leisure time behaviour and is informative for further research
and interventions.

Consistent with previous studies that have combined diary and objective data, there
may be errors in the children’s report of their activities and consequent MVPA classification
[55]. For example, children may have recorded time spent with friends when in fact they
were also under the supervision of an adult. In addition a significant proportion
of time between 15:00 and 22.00 was unaccounted for due to missing diary entries reporting
who the children were with. Diary records were not available for 40.5% of girls and
38.3% of boys after school time, and the proportion of missing diary data increased
by hour up until bedtime. The participants were asked to record what they did after
school, and as such periods where their behaviour was unstructured or intermittent
may be more difficult to report [56]. This may especially be the case for children who lack the cognitive and linguistic
ability to describe their behaviour [57]. Unstructured activity may be more likely to reflect low intensity physical activity
so a greater proportion of this might be missing data. This is supported by the fact
that missing diary data contributed disproportionally fewer minutes of MVPA. However,
approximately one third of MVPA was not recalled and described by children in their
diary. Examining the source of this unreported physical activity should be the subject
of further research.

It is also likely that there were errors in the differentiation of physical activity
location by the GPS receiver. The GPS signal can be lost when outdoors and although
children were trained to turn the GPS on when leaving school it is possible that some
delay may have occurred leading to loss of outdoor data. Some outdoor data may therefore
erroneously be classified as indoors. The present study was cross sectional, only
recorded after school weekday activities and did not adjust for clustering within
schools. Longitudinal work is required to fully understand the impact of the variables
explored here, particularly the influence of the companionship of other children on
independent mobility and unstructured outdoor physical activity. Whilst at present
it is clear that children’s outdoor time with friends represents a very small proportion
of leisure time, this represents an important intervention target. This is because
of the potential for change during the after school period, the greater accumulation
of MVPA during time spent in this context, the additional social benefits of this
type of activity [20], and the harmful effects of sedentary behaviours occurring indoors [14].

Conclusions

This study indicates that children spend most of the after school period indoors alone
or with parents and very little time outdoors playing with other children. However,
that time which is spent outdoors with friends makes the greatest contribution towards
outdoor MVPA. Time outdoors with other children was most strongly associated with
MVPA whereas time spent alone was not associated with MVPA either indoors or outdoors.
In addition to promoting active time indoors, strategies to foster neighbourhood friendship
groups and remove barriers which restrict time outdoors should be investigated further
and considered as components of larger multi-level interventions to promote physical
activity.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

MP drafted the initial manuscripts and conducted the analyses. All other authors contributed
to the design of the project and the writing of the manuscript. All authors read and
approved the final manuscript.

Acknowledgements

The authors are very grateful to the participants and their families who gave their
time to the study. We would also like to acknowledge all members of the PEACH Project
team not listed as co-authors of this paper. This work was supported by the National
Prevention Research initiative [G0501311] and World Cancer Research Fund (WCRF UK).

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